Prior systems for collecting blood rely on venous pressure and hydrostatic pressure to cause blood to flow from a donor's arm. A phlebotomy needle that is connected by tubing to a blood collection bag containing anticoagulant is inserted into a donor's arm. Hydrostatic pressure is achieved by positioning the collection bag about 18 inches below the level of the donor's arm and venous pressure is controllable to some extent by varying the pressure in a cuff attached to the donor's arm above the venipuncture site and, by directing the donor to alternately flex and relax his/her hand. Older collection apparatus used a relatively large needle (e.g., 16 gauge) which, when inserted, caused appreciable patient discomfort. Also, during the collection process, the non-anticoagulated whole blood drawn from the donor had to pass through the phlebotomy needle and along a length of tubing before it reached the anticoagulant in the blood collection bag. If the rate of flow of blood through the tubing was not maintained high enough, clotting could occur, reducing the usefulness of the collected blood.
To avoid the aforementioned problems, there has been developed relatively recently blood donation apparatus which utilizes a peristaltic or roller pump to withdraw whole blood from a donor through a much smaller (e.g., 19 gauge) phlebotomy needle, and to pump the blood through a tube leading to the collection bag. Anticoagulant flowing through a second tube leading from an anticoagulant source is mixed with the whole blood right at the outlet of the phlebotomy needle. The anticoagulant tube passes through the same pump head that draws the whole blood from the donor, so that the ratio of blood to anticoagulant is determined by the ratio of the diameter and elastic properties of the drawn blood tube with respect to those of the anticoagulant tube. Such a blood donation apparatus is disclosed in U.S. Pat. No. 4,385,630.
While that patented apparatus is a considerable improvement over the prior blood collection apparatus, it still has certain drawbacks. For example, it must be primed manually so that anticoagulant fills the anticoagulant tube down to the phlebotomy needle. Also, it employs a peristaltic pump with a single roller pump head acting on both the blood tube and anticoagulant tube. Therefore, the blood-to-anticoagulant ratio depends upon the tubing characteristics, making it difficult to change that ratio. Still further, the disposable blood collection set used in that prior blood donation apparatus is relatively difficult to install in the pump unit such that the drawn blood and anticoagulant tubes are properly positioned on the unit's pump head.
That patented blood donation apparatus is further disadvantaged because it is only able to collect a set volume of whole blood. Often, it is desirable to have the option of collecting different blood volumes. For example, in some cases, it may be necessary to collect a specific mass of red blood cells (RBC) based on the donor's known hematocrit, i.e., the percentage by volume of RBC in drawn whole blood. Even if the target volume of RBC is always the same in such cases, the volume of whole blood to be drawn will vary from donor to donor.
Finally, that known apparatus does not provide a record of the collection procedure and does not positively correlate the drawn blood with the donor of that blood. Therefore, there is always the possibility of the collected blood being mis-identified and misused.